Acoustics Flashcards
Sound
An auditory disturbance in a medium caused by a vibrating source
The disturbance must be capable of causing vibrations in a receiver
The receiver can be the auditory system
Prerequisites for Sound Production
A source of energy (lungs)
A vibrating source that will generate an audible pressure wave (vocal folds)
A medium of transmission (air)
Hearing Loss Levels
Normal Hearing Levels = -10 dB and 25 dB Mild Hearing Loss = 26dB to 40 dB Moderate Hearing Loss = 41 dB to 55 dB Moderately-Severe Hearing Loss = 56 dB – 70 dB Severe Hearing Loss = 71 dB – 90 dB Profound Hearing Loss = 91 and greater
Hearing Loss and Language
Hearing loss > 60 dB limits perception of sound – child generally not able to produce normal oral language without intervention
Issues with pitch, loudness and resonance common in persons with HL > 60dB
> 90 dB – profoundly deaf and will not develop speech and language skills without educational and therapeutic intervention
The Role of Hearing in Language Development
Hearing is the most efficient way to develop spoken communication and literacy.
When we talk about hearing we talk about auditory brain development.
Technology is really a brain-access tool.
Stimulation of the auditory brain will permit it to develop. If the auditory brain is not stimulated, that area will be taken over by other skills, primarily visual.
Children need to hear 46 million words by age 4.
20,000 hours of listening is the basis for reading.
Children with hearing loss need three times the exposure to learn new words and concepts.
Simple Harmonic Motion
Pure tones
Periodic vibratory movement in which the vibratory body moves directly from one point of maximum displacement to the other point of maximum displacement
The forces of elasticity and inertia are simultaneously at work; As elasticity increases/inertia decreases and vice versa
Produces a sine wave – graph of simple harmonic motion
Inertia
Tendency for motion or lack of motion to continue
Elasticity
the restoring force that causes an elastic medium to bounce back when stretched or displaced
Periodic Tone
Sound waves in which the pattern of vibration, however complex, repeats itself exactly over time
Simple – One component frequency – a pure tone
Complex – Two or more component frequencies that are harmonically related: a fundamental frequency plus harmonics – A complex tone
Velocity
speed in a certain direction
Light travels faster than sound
A faint sound travels as fast as a loud one as long as temperature remains the same
Sound travels faster on a hot day vs. a cold day
Maximum velocity
reached each time the swing seat passes over its original resting place
Damping
decrease in the amplitude of displacement over time
the decrease in motion after force has been removed which will return the movement to the rest point
Complex Tone
Sound having more than one sine wave component
Periodic
Aperiodic
Aperiodic Tone
Sound wave in which the vibration is random and displays no repeatable pattern
Simple – Does not exist
Complex – Two or more component frequencies not harmonically related: no fundamental frequency, no harmonics - NOISE
Harmonic
An oscillation whose frequency is an integral multiple of the fundamental frequency
Example – violin String is 100 Hz Each half vibrates at 200 Hz Each third at 300 Hz And so on
Each tone generated by the complex vibration is called a harmonic
Waveform
a graphic representation of a vibratory event showing amplitude versus time
Frequency
is the number of vibratory cycles per second – measured in Hertz (Hz)
Healthy human listeners can detect vibrations as low as 20 Hz and as high as 20,000 Hz
Subsonic - Vibrations too low to be heard
Ultrasonic – vibrations too high to be heard
Frequencies most important for detection of the speech signal – 100 – 5000 Hz
Frequency
Number of completed vibratory cycles per second
Expressed in Hertz (Hz)
Period – time taken to complete each cycle
Healthy human listeners can detect vibrations as low as 20 Hz and as high as 20,000 Hz
Subsonic - Vibrations too low to be heard
Ultrasonic – vibrations too high to be heard
Frequencies most important for detection of the speech signal – 100 – 5000 Hz
Frequency
Number of completed cycles per second
Expressed in Hertz (Hz)
Period – time taken to complete each cycle
Wavelength
The length of a sound wave is the distance in space that one cycle occupies
Wavelength
The length of a sound wave is the distance in space that one cycle occupies
depends on the frequency of the vibration and the velocity of sound wave propagation in the medium (high frequency sounds occupy less space than low frequency sounds)
The medium through which sound travels – solids, liquids, gases
Resonance
Vibratory response to an applied force
Resonator
Something that is set into vibration by the action of another vibration
Does not initiate sound
Vibrates in sympathy to sounds created externally to them
The larger the vocal tract/cavity, the lower the frequencies to which they will resonate
The smaller the vocal tract/cavity, the higher the frequencies to which they will resonate
Acoustic Resonators
contain air
A body of air will resonate in response to sound containing frequencies
Musical instrument
Vocal tract
Ear canal
Clinical Applications of Acoustic Knowledge
Normal vocal fold vibration is periodic; aperiodicity may reflect vocal pathology
Acoustic analysis may reveal characteristics of speech that are not perceived auditorily
Audiology – uses pure tones to assess hearing acuity
